Heat the egg white in a water bath. Cream butter, 1/2 teaspoon salt and sugar. Stir in the egg white. Mix flour and corn semolina and fold in. Spread the mixture in a circle (28 cm diameter) on a baking tray lined with baking paper.
Bake in the preheated oven (electric oven: 175 °C/ gas: level 2) for about 15 minutes. Turn out onto an upside-down dish and allow to cool. Peel the avocado, remove the stone and dice the flesh.
Add lemon juice and puree with the cutting stick of the hand mixer. Peel and finely dice the shallot. Stir the yoghurt and diced shallots into the avocado puree and season to taste with salt and cayenne pepper.
Pour dip into a bowl. Peel and finely dice an onion. Finely grate the toast. Knead minced meat, toast, diced onion and egg well. Season with salt, pepper, paprika and chilli powder.
Form small balls. Heat oil in a pan and fry the balls in it until golden brown. Clean, wash and cut the salad into strips. Peel the remaining onions and cut them into rings. Drain beans and corn.
Mix the salad ingredients and meatballs and arrange in the cornflake dish. Dust with paprika.